Fix OpenApiJsonSchema array parsing

[BrennanConroy]

Fixes #62023

We weren't reading before calling the recursive function which meant we'd never advance the Utf8JsonReader and always be in the state reader.TokenType == JsonTokenType.StartArray

[captainsafia]

LGTM! Comment inline about possibly adding coverage for custom converts that emit objects instead of arrays.

[BrennanConroy]

/backport to release/9.0

[github-actions]

Started backporting to release/9.0: https://github.com/dotnet/aspnetcore/actions/runs/15282951411

[github-actions]

@BrennanConroy backporting to "release/9.0" failed, the patch most likely resulted in conflicts:

$ git am --3way --empty=keep --ignore-whitespace --keep-non-patch changes.patch

Applying: Fix OpenApiJsonSchema array parsing
Using index info to reconstruct a base tree...
M	src/OpenApi/src/Schemas/OpenApiJsonSchema.Helpers.cs
M	src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs
Falling back to patching base and 3-way merge...
Auto-merging src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.ParameterSchemas.cs
Auto-merging src/OpenApi/src/Schemas/OpenApiJsonSchema.Helpers.cs
CONFLICT (content): Merge conflict in src/OpenApi/src/Schemas/OpenApiJsonSchema.Helpers.cs
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
hint: When you have resolved this problem, run "git am --continue".
hint: If you prefer to skip this patch, run "git am --skip" instead.
hint: To restore the original branch and stop patching, run "git am --abort".
hint: Disable this message with "git config set advice.mergeConflict false"
Patch failed at 0001 Fix OpenApiJsonSchema array parsing
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!